Show a direnv error after bazel clean (#3)

Fixes #2

bazel_env.bzl

@@ -285,6 +285,9 @@ def _bazel_env_rule_impl(ctx):
         is_executable = True,
         substitutions = {
             "{{name}}": ctx.label.name,
+            # We assume that the target is in the main repo and want the label to look like this:
+            # //:bazel_env
+            "{{label}}": str(ctx.label).removeprefix("@@"),
             "{{bin_dir}}": unique_name_tool.dirname,
             "{{unique_name_tool}}": unique_name_tool.basename,
             "{{has_tools}}": str(bool(tool_infos)),

examples/.envrc

@@ -1 +1,6 @@
+# Generated by 'bazel run //:bazel_env'
+watch_file bazel-out/bazel_env-opt/bin/bazel_env/bin
 PATH_add bazel-out/bazel_env-opt/bin/bazel_env/bin
+if [[ ! -d bazel-out/bazel_env-opt/bin/bazel_env/bin ]]; then
+    log_error "ERROR[bazel_env.bzl]: Run 'bazel run //:bazel_env' to regenerate bazel-out/bazel_env-opt/bin/bazel_env/bin"
+fi

status.sh.tpl

@@ -25,7 +25,12 @@ else
     cat << 'EOF'
 ⚠️ {{name}}'s bin directory is not in PATH. Please add the following snippet to a .envrc file next to your MODULE.bazel file:
 
-    PATH_add {{bin_dir}}
+# Generated by 'bazel run {{label}}'
+watch_file {{bin_dir}}
+PATH_add {{bin_dir}}
+if [[ ! -d {{bin_dir}} ]]; then
+    log_error "ERROR[bazel_env.bzl]: Run 'bazel run {{label}}' to regenerate {{bin_dir}}"
+fi
 
 Then allowlist it with 'direnv allow .envrc'.
 EOF